Error connecting to database with SQLAlchemy and fastAPI

Question

I have this setting on a fastAPI small application:

host_server = os.environ.get('host_server', 'localhost')
db_server_port = urllib.parse.quote_plus(str(os.environ.get('db_server_port', '5432')))
database_name = os.environ.get('database_name', 'mydatabasename123')
db_username = urllib.parse.quote_plus(str(os.environ.get('db_username', 'myusername123')))
db_password = urllib.parse.quote_plus(str(os.environ.get('db_password', 'mypassword123')))
ssl_mode = urllib.parse.quote_plus(str(os.environ.get('ssl_mode', 'prefer')))
DATABASE_URL = 'postgresql://{}:{}@{}:{}/{}?sslmode={}'.format(db_username, db_password, host_server, db_server_port,
                                                               database_name, ssl_mode)

database = databases.Database(DATABASE_URL)

locally it works, but when I try to deploy it to heroku, I change some things. I am use the DATABASE_URL env variable provided on Heroku:

DATABASE_URL = 'postgres://...'
database = databases.Database(DATABASE_URL)

or doing

DATABASE_URL = os.environ.get('DATABASE_URL')

database = databases.Database(DATABASE_URL)

metadata = sqlalchemy.MetaData()

engine = sqlalchemy.create_engine(
    DATABASE_URL, pool_size=3, max_overflow=0, echo=True
)

logs give me:

: at=error code=H10 desc="App crashed" method=GET path="/" 

Answer 1

"postgres" is no longer accepted as a dialect name in SQLAlchemy. The correct form is "postgresql", as you are using locally:

DATABASE_URL = 'postgresql://...'

Using 'postgres://...' raises

sqlalchemy.exc.ArgumentError: Could not parse rfc1738 URL from string 'postgres//...'

This change was introduced in SQLAlchemy 1.4.0b1